[Tagging] Using multipolygons to map bays in Alaska

Kevin Kenny kevin.b.kenny at gmail.com
Sat Nov 17 21:28:34 UTC 2018


On Sat, Nov 17, 2018 at 3:36 PM Paul Allen <pla16021 at gmail.com> wrote:

> You point out that neither a new polygon that shares nodes with coastline
> ways nor a complex
> relationship are going to play nicely with the toolchain.  Being a bear of
> little brain, and lazy to
> boot, my first thought would be a crude polygon approximating the
> coastline.  It would have few
> enough nodes that it would be renderable but approximate the coastline
> sufficiently well for label
> placement.  Provided the carto didn't render the bay in a different colour
> or with a visible border it
> would handle label placement nicely (particularly if the renderer's
> placement algorithms
> improved in the future) without looking fugly.  I must be wrong about
> this, though, because I
> recall an earlier post in this thread pointing out where somebody had done
> something very like
> that and denounced it as a crime against humanity.
>

That's what I meant when I discussed 'generalizing' the way.
'Generalization' is a GIS-speak term for reducing point count and
resolution to make an object suitable for rendering at larger scale.

So all that appears to leave is a node with sub-tags of bay=small,
> bay=intermediate, bay=large and
> bay=supersize to control the size of the label whilst the mapper controls
> the position of the label by
> guessing where the node ought to go.  I still like a polygon even if the
> water in the bay looks no
> different from the ocean because using the query tool on the polygon will
> bring up an approximation
> to the extent of the bay.
>

It is sounding as if Frederik and Christoph are willing to tolerate limited
experiments as long as we mostly don't damage the coastline, and keep our
areas small enough not to break the toolchain. I'm satisfied with that as
an answer for now. If using areas has the advantages that you and I think
it does, then it'll win out over time. If it has the difficulties that
Frederik and Christoph fear, then mappers won't adopt it and the discussion
will be moot.

And I surely sympathize with their woes about managing large objects! I've
had to repair ones like Lake Huron (relation 1205151, but please don't
overload the server by trying to fetch it!) a time or two, myself, and it's
painful, what with the server timeouts and all. (There was a serious
proposal floated at one point to make the Great Lakes 'natural=coastline',
for just that reason, but I seem to recall that it foundered on topology.
The only way to handle it would have been to extend the coastline all the
way up the St. Lawrence, Niagara, Detroit, St. Clair, Mackinac and St.
Mary's Rivers, and make all the islands in the Great Lakes 'coastline' as
well - effectively inverting the topology of everything in contact with the
lakes.

So for the moment, I'll confine any experiments to objects the size of
Jamaica Bay, while leaving Hudson Bay or the Gulf of Mexico, or even the
Long Island Sound, to a later time.

I'm convinced that sooner or later we will need a better general solution
than just placing a node - as I said, I'd really like a paper map of
Helsinki or Tallinn to label the Gulf of Finland. But I don't yet have
really good ideas about how to upgrade the technology to get there with
large objects - a few half-baked ones, but I'm rather a long way from
trying them yet.
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